The proliferation of mammalian cells is controlled by polypeptide growth factors. Treatment of quiescent fibroblasts with mitogenic growth factors results in the rapid activation of a set of immediate early genes whose expression is thought to mediate the proliferative effect of the stimulating growth factor. One such gene, cyr61, is activated on the transcriptional level by serum growth factors and by the viral oncogene v- src. cyr61 encodes a cysteine-rich heparin-binding protein that associates with the extracellular matrix and the cell surface. The biochemical features of Cyr61 fit the profile of a classical polypeptide growth factor. Developmental expression of cyr61 correlates with chondrogenesis, and ectopic expression of cyr61 in transgenic mice leads to skeletal abnormalities, suggesting that Cyr61 might play a role in regulating aspects of chondrogenesis that form the embryonic skeleton. Recent studies relate Cyr61 to a newly discovered family of growth regulators, including connective tissue growth factor, a mitogen and chemoattractant, and Nov, a cellular oncoprotein deregulated in virus-induced nephroblastomas. These results suggest that Cyr61 is a member of an emerging family of cytokines, and may function in regulating aspects of growth, differentiation, and development. This proposal aims to investigate the biological functions of Cyr61 and its related family members. Five approaches will be taken to accomplish this objective: 1. Specific reagents will be developed for Cyr61 and its closely related family member Fisp12; the Cyr61 protein will be expressed, purified, and characterized. 2. Bioassays will be developed to test whether Cyr61 acts as a mitogen, a chemoattractant, and/or a differentiation factor. Its oncogenic potential will be assessed. 3. The mechanisms through which Cyr61 acts will be examined. The possibility that it interacts with a specific cell surface receptor will be investigated; this putative receptor will be identified and characterized. 4. The expression of cyr61 and the related gene fisp12 during development will be examined. Their expression during processes such as wound healing will also be investigated. 5. Aberrant expression of cyr61 and its mutated forms in transgenic mice will be used to test hypotheses regarding Cyr61 function in the context of the living animal. Information obtained using these approaches should help to elucidate the biochemical activities and biological roles of this new family of growth regulators.